Thousands of protesters gathered in Sydney on Sunday to urge leaders to take action on climate change, with environmentalist Tim Flannery declaring the event the "biggest climate march this country's ever seen".

Organisers said 45,000 people attended the rally, which began in The Domain before a march down Macquarie Street to the Opera House, following speeches and performances calling on those at the Paris climate summit to shift more rapidly to renewable energy.

The rally observed a minute's silence to acknowledge those most affected by climate change, culminating in the playing of a didgeridoo. Former Voice contestant Darren Percival also sang.

Following the performances at The Domain, the march made its way through the streets of Sydney, with people co-ordinated into eight coloured "blocs", symbolising the various communities represented at the march.

A former Australian of the Year and renowned environmentalist, Dr Flannery spoke at the Sydney rally, saying: "At least from where I'm standing this looks like the biggest climate march this country's seen."

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David Sindel, 30, and friends - dressed as coral, anemones and sea grass - said: "I'm here because I care about the planet and the environment.

"It can sometimes be depressing the lack of action but then you come to an event like this and see how many others care as well."